Grebes

Grebes

Grebes are an old group, having been inhabitants of lakes and marshes for Around 70 million years, and have representative species on all continents except Antarctica.

Thanks to anatomical adaptations grebes are well suited to the rigors of aquatic life and underwater hunting. They have a dense plumage of some 20,000 feathers to keep them dry and warm. Their feet are at the extreme hind end of the body the tail is reduced to a downy tuft and has exceptional flexibility in the ankle and toe joints, allowing the feet to pivot in all directions and to be used, simultaneously, as “pad-dales” and “rudders.”

The lobes on the toes further aid the maneuverability of a diving grebe can move at about 2m (6.6ft) a second and turn extremely quickly. Grebes can sink lowing the water by expelling the insulating air from between their feathers and emptying their air sacs (reservoirs of air): this reduces the energy needed to keep them submerged and allows them to dive silently when hunt-in and to hide submerged when frightened. Dives typically last up to 40 seconds.

Feet placed so far back make even stand-in difficult: grebes only stand at the nest and, if obliged to reach nests “stranded” befalling water levels, frequently fall when try-in to walk; they need a long take-off run across the water to become airborne on their long thin wings, but fly quickly with rapid beats and trailing feet; they maneuver poorly in flight. Grebes rarely fly except on migration and a few species are flightless. They may migrate long distances, often fly-in at night, when they sometimes mistake wet roads for rivers, land on them, and become stranded.

Grebes are carnivorous, eating mainly insects and fish but also some mollusks and crustacea, taking the latter from off and around aquatic water plants or, more rarely, from the bottom. The larger species chase fish, and the Western grebe of North America spears (rather than grabs) fish with its dagger-shaped bill. Grebe species form” guilds” of aquatic carnivores, vying with each other to exploit foods more efficiently.

In Eurasia, for example, the Great crested grebe occurs mostly in open water, eating fish that it usually catches within a few meters of the surface, whereas little grebes occur on small ponds covered with floating water plants which they are small enough to dive among. Intermediate-sized species, such as Red-necked and Slovenian grebes, may be restricted to lake habitats where they do not compete with larger species. For example, the Slovenian is the only grebe that breeds in Iceland and there it eats many fish as well as insects, but in Alaska, it restricts its diet largely to insects and fish fry due to competition from the Red-necked grebe; similarly, in eastern Siberia and Alaska, a long-billed race of the Red-necked grebe has evolved which takes larger fish than its European counterpart which has to compete with. Great crested grebes for food.

The courtship behavior of grebes is very striking, involving complex sequences of elaborate, ritualized postures and, particularly in Pedicels species, much use of the erectile feather ruffs and tufts on the head. Many elements of these complex sequences are shared by many species and considerable progress has been made both in understanding animal behavior and grebes’ evolutionary histories by comparing details of their courtships. The Hooded grebe has a close relationship to Black-necked, Silver, and Puma grebes.

The crucial role that these displays serve in pair formation has been emphasized by recent findings on the Western grebe: This species occurs in two color variants (morphs) that breed in mixed colonies, but only birds of the same color morph will pair together and this segregation is achieved by each morph using a distinctly different “advertising call” to initiate courtship. An interesting feature of grebe displays is that males and females may reverse their normal roles, even to the extent of reverse mountings.

Most grebes are aggressively territorial, but some species nest in colonies. The timing of breeding is flexible grebes seem adapted to exploit opportunistically a good food supply rather than being tied to a specific season. In Africa, little grebes may appear and start breeding within a few days of unpredictable rain storms producing temporary flood ponds. The nests are mounds of aquatic vegetation, usually anchored in emergent waterweeds. The chicks hatch asynchronously and are brooded on their parents’ backs, even when their parents dive.

See more: Loons